"Over your shoulder" pose is often required for a model during a photo shoot, and "Throwing salt over your shoulder" came about because people once believed the devil stood behind your left shoulder waiting for you to make a mistake or to influence you into making a mistake. Throwing some of the spilled salt over your left shoulder would be throwing it into the Devil's eyes, thus blinding him to your mistake. Blind is part of the fashion system in front of the excessive thinnes of a lot of models, forced to fit into small sizes to work.